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What’s a KWH?

A recent review of the experience renting an EV and using public chargers asks “What’s a KWH?” That’s an interesting question, as we’re all used to gallons of gas. Here’s my oversimplified explanation.

Gas is sold by the gallon. A car gets anywhere from 20 to 50 miles per gallon. Electricity is sold by the Kilowatt Hour (KWH), which is one kilowatt (1000 watts) for an hour. (Think of 10 100 watt incandescent bulbs turned on for an hour.) An EV gets anywhere from 3 to 4 miles per KWH.

As a rule of thumb, 10 KWH is takes your EV the same distance as a gallon of gas takes a car, and it makes the math easy – just move the decimal point. If you can charge at home for 12 cents/KWH (the national average) that’s like $1.20/gal of gas. In San Diego, I can charge overnight at home for 22 cents/KWH, or $2.20/gal. If I pay 50 cents/KWH at a public charger, that’s like $5.00/gal.

This is a rough comparison, and it will vary from car to car and charger to charger. My Chevy Volt gets 3.5 miles/KWH or 39 miles/gallon of gas, depending on weather and hills. So it’s not exact. But neither is 4 liters/gallon, and it’s still a useful rule of thumb.